Recommendation ITU-T H.265 (also known as HEVC) for “coding of moving video,” published in April 2015 by the ITU, which is incorporated herein by reference in its entirety, in Annex D.2.32 “Colour remapping information SEI message syntax” and D.3.32 “Colour remapping information SEI message semantics,” typically referred to as “CRI messaging,” describes the syntax for providing supplemental enhancement information (SEI) to enable a decoder to remap the reconstructed color samples of the output pictures. It uses a color remapping model that includes a first (“pre”) piece-wise linear function, a 3×3 matrix, and a second (“post”) piece-wise linear function, thus allowing remapping color values to a specific color volume of a targeted display.
In parallel with the MPEG/ITU standardization processes, the society of motion picture and television engineers (SMPTE) has also defined a number of Recommendations related to communicating metadata for color volume transforms. For example, SMPTE ST 2096-30:2016, “Dynamic Metadata for Color Volume Transform—Application #3,” Jul. 6, 2016, which is incorporated herein by reference, which is part of the SMPTE 2096 family of recommendations, defines the syntax for dynamic metadata generated when a content creator produces a “standard dynamic range (SDR) grade” master from an original “high dynamic range (HDR) grade” master. These metadata can be used by a downstream SDR rendering device to provide a color volume transform so that the displayed image closely matches the artistic intent in the “SDR grade” image. As used herein, the term “metadata” relates to any auxiliary information that is transmitted as part of the coded bitstream and assists a decoder to render a decoded image. Such metadata may include, but are not limited to, color space or gamut information, prediction parameters, reference display parameters, and auxiliary signal parameters, as those described herein.
While Annex D of H.265 supports a number of metadata defined by earlier SMPTE ST-2094 recommendations, it does not carry all the required metadata for the latest versions. To improve existing decoding schemes, as appreciated by the inventors here, improved techniques for utilizing the existing CRI syntax for communicating color remapping information is required.
The approaches described in this section are approaches that could be pursued, but not necessarily approaches that have been previously conceived or pursued. Therefore, unless otherwise indicated, it should not be assumed that any of the approaches described in this section qualify as prior art merely by virtue of their inclusion in this section. Similarly, issues identified with respect to one or more approaches should not assume to have been recognized in any prior art on the basis of this section, unless otherwise indicated.